Method for tuning epitaxial growth by interfacial doping and structure including same

ABSTRACT

A method that allows for uniform, simultaneous epitaxial growth of a semiconductor material on dissimilarly doped semiconductor surfaces (n-type and p-type) that does not impart substrate thinning via a novel surface preparation scheme, as well as a structure that results from the implementation of this scheme into the process integration flow for integrated circuitry are provided. The method of the present invention can by used for the selective or nonselective epitaxial growth of semiconductor material from the dissimilar surfaces. More specifically, the invention comprises a method for counterdoping of n-FET and/or p-FET regions of silicon circuitry during the halo and/or extension implantation process utilizing a technique by which the surface characteristics of the two regions are made similar with respect to their response to wet or dry surface preparation and which renders the two previously dissimilar surfaces amenable to simultaneous epitaxial growth of raised source/drain structures; but not otherwise affecting the electrical performance of the resulting device.

FIELD OF THE INVENTION

The present invention relates to semiconductor device fabrication, andmore particularly to a method that allows for simultaneous, uniformselective or non-selective epitaxial growth of a material from similaror dissimilar surfaces by controlling interfacial doping. The presentinvention also relates to the semiconductor structure that is obtainedusing the method of the present invention.

BACKGROUND OF THE INVENTION

Selective epitaxial growth is the critical unit process for theformation of semiconductor structures including raised source/drain(RSD) regions used to enable silicon integrated circuit technology, suchas complementary metal oxide semiconductor (CMOS) structures on a bulkSi-containing semiconductor or a silicon-on-insulator (SOI) and bipolardevices. As with all selective epitaxial processes, the growth of theRSD is highly dependent on the nature of the surface from which it isgrown and, in turn, the pre-epitaxy preparation of that surface. Forexample, in some bulk silicon and in some partially depleted SOI (PDSOI)and fully depleted SOI (FDSOI) CMOS integration schemes, it is highlydesirable to implant the halo and extension implants prior to the growthof the RSD. This leads to dissimilar surfaces in the n-field effecttransistor (n-FET) and p-field effect transistor (p-FET) regions. Inparticular, the p-FET and the n-FET regions have different surfacecharacteristics, in terms of their response to various surfacetreatments and rate of subsequent epitaxial growth. That is, in thesetwo regions the surface preparation and epitaxial growth are generallydependent on the dopant type in those regions.

In order to simultaneously grow selective epitaxial films in both n-FETand p-FET regions, a surface preparation technique, which comprisestechniques such as wet etching, plasma treatment, thermal processing,vapor treatment and other surface modifications, is needed thateffectively removes undesired surface films from the desired growthregions.

As the surface characteristics are rendered dissimilar by nature of theimplants (including, but not limited to: halo implant and/orsource/drain extension implant), one of two results is often afforded:either a less aggressive surface preparation is imparted that does noteffectively remove undesired films from one region leading to inadequatesimultaneous growth in one region; or, a more aggressive surfacepreparation is used which allows simultaneous growth, but results inexcessive thinning of the underlying crystalline or polycrystallinesurface from which the epitaxial film is grown.

In view of the drawbacks mentioned with prior art processing of RSDregions, there is a need for providing a method which allows forsimultaneous, uniform selective or non-selective epitaxial. growth of amaterial from surfaces, e.g., regions, having similar or dissimilarsurface characteristics, without imparting substrate thinning.

SUMMARY OF THE INVENTION

The present invention describes a method that allows for simultaneous,uniform selective or non-selective epitaxial growth of a material onsimilar or dissimilar surfaces that does not impart substrate thinningvia a novel surface preparation scheme, as well as a structure thatresults from the implementation of this scheme into the processintegration flow for integrated circuitry. The dissimilar surfaces aretypically doped surfaces such as, but not limited to: the source/drainregion and/or the gate region of a field effect transistor (FET). Whendissimilar surfaces are present, the method of the present inventiontypically provides a way to modify one of the dissimilar surfaces viainterfacial doping such that it has substantially the same growth rateof an epitaxial material and response to surface preparation as one ofthe other dissimilar surfaces that are not subjected to the interfacialdoping. When similar surfaces are present, the method of the presentinvention typically provides a way to induce a difference in one surfaceregion via interfacial doping such that epitaxial growth of a materialin that surface region is prevented.

More specifically, the invention comprises a method for counterdopingvia interfacial doping of n-FET and/or p-FET regions of semiconductorcircuitry during the halo and/or extension implantation processutilizing a technique by which the surface characteristics of the tworegions are made similar with respect to their response to wet or drysurface preparation and which renders the two previously dissimilarsurfaces amenable to simultaneous epitaxial growth of RSD structures;but not otherwise affecting the electrical performance of the resultingdevice.

The counterdoping method involves implantation of one or more implantspecies using selected energy and dose conditions in the n-FET and/orp-FET region that effectively affords surface characteristics of thedoped region similar to that of its counterpart such that any subsequentpre-epitaxy surface preparation can be universal in affording similarsurfaces for uniform, simultaneous epitaxial growth, but still allowsfor appropriate device performance. The energy and dose of the dominantimplant species may be adjusted to afford desired performance. Thecounterdoping conditions are chosen to render only the surface affectedto make the dissimilar surfaces similar in their response to surfacepreparation and therefore are generally of low energy and low dose.

Additionally, counterdoping can be employed to selectively inhibitepitaxial growth on pre-determined regions by using the same concept.

In broad terms, the method of the present invention comprises:

providing a structure having at least two regions, wherein said at leasttwo regions have either similar or dissimilar surface characteristics interms of their response to surface treatments and rate of epitaxialgrowth; and

introducing an interfacial dopant into at least one of said at least tworegions to modify the surface characteristic within that region to beeither the same or different from the other region not including saidinterfacial dopant, with the proviso that when the substrate has regionsof similar surface characteristics, then the interfacial dopant providesa region that has a dissimilar surface characteristic than the otherregion, and when the substrate comprises dissimilar surfacecharacteristics, then the interfacial dopant provides a region havingthe same surface characteristic as that of the other region.

Following the introduction of the interfacial dopant, the inventivemethod contemplates the use of various surface treatment steps and/orepitaxial growth of a material from the regions including at least saidinterfacial dopant. The interfacial dopant that is introduced maycomprise a counterdopant species or a neutral species. The interfacialdopant may be introduced via ion implantation, plasma immersion or byfirst providing a material layer including said interfacial dopant on asurface of said structure and then annealing to cause outdiffusion ofthe interfacial dopant from the material layer into the structure.

The method of the present invention can be implemented into existingsemiconductor technologies including, for example, during the CMOSprocessing of FETs and the subsequent formation of RSD regions.

In addition to the method described above, the present invention alsorelates to the semiconductor structure that is formed utilizing thesame. In broad terms, the semiconductor structure of the presentinvention comprises

at least one material region that is doped or undoped, wherein said atleast one material region further includes an interfacial dopant regionthat changes the surface characteristic of said at least one materialregion in terms of its response to surface treatments and rate ofepitaxial growth compared with another material region.

In some embodiments, the at least one material region may furtherinclude an epitaxial material layer located thereon, wherein saidinterfacial dopant region is located between said at least one materialregion and said epitaxial material region.

In one preferred embodiment of the present invention, the at least onematerial region may comprise the source/drain area and/or the gateregion of at least one FET.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1D are pictorial representations (through cross sectional views)depicting the basic processing steps that are employed in one embodimentof the present invention.

FIGS. 2A-2C are pictorial representations (through cross sectionalviews) depicting the basic processing steps that are employed in yetanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides a method of interfacial controlfor selective or non-selective epitaxial growth for semiconductorstructures as well as the structures that result from such a method,will now be described in greater detail by referring to the drawingsthat accompany the present application. It is noted that the drawings ofthe present invention are provided for illustrative purposes and as suchthey are not drawn to scale. It is also noted that the followingdescription and drawings describe the inventive method being implementedin fabricating a CMOS structure including RSD. Although such anembodiment is described and illustrated, the inventive method can beused for fabrication of other semiconductor devices, which include theepitaxial growth of a material layer from at least one material regionthat is doped or undoped.

FIG. 1A shows an initial structure 10 that can be used in the presentinvention. As shown, the initial structure 10 includes a semiconductorsubstrate 12 having patterned gate regions 16A and 16B located on asurface of the semiconductor substrate 12; each patterned gate region16A and 16B includes a gate dielectric 18 and a gate conductor 20. Thepatterned gate regions 16A and 16B are located in at least two regions50A and 50B that have dissimilar surface characteristics in terms oftheir response to surface treatments and rate of epitaxial growth.Specifically, the regions having dissimilar surface characteristics mayinclude a doped region 14A and 14B that are of opposite conductivitytype. The doped regions 14A and 14B are typically an extension implantregion that are formed utilizing a conventional extension ionimplantation that is well known in the art. The doped regions, which canalso include halo implants, are part of the FET's source/drain region.The doped surface 14A may include n-type dopants or p-type dopantsdepending on the type of semiconductor structure that is beingfabricated therein, while the doped surface 14B includes the oppositedopant type. As such, the patterned gate region 16A may comprise ap-type FET having p-type regions or an n-type FET having n-type regions.The patterned gate region 16B has the opposite conductivity as that ofthe patterned gate region 16B.

Each patterned gate region present in the initial structure may beformed utilizing conventional deposition, lithography and etching or aconventional gate replacement process can be used in forming the same.It is emphasized that the processing steps of forming the patterned gateregions are well known in the art and, as such, details concerning thefabrication of the patterned gate regions are not provided herein.

The semiconductor substrate 12 employed in the present inventioncomprises any semiconducting material including, but not limited to: Si,Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs, InP and all other III/V or II/VIcompound semiconductors. The semiconductor substrate 12 may alsocomprise an organic semiconductor or a layered semiconductor such asSi/SiGe, a silicon-on-insulator (SOI) or a SiGe-on-insulator (SGOI). Insome embodiments of the present invention, it is preferred that thesemiconductor substrate 12 be composed of a Si-containing semiconductormaterial, i.e., a semiconductor material that includes silicon. Thesemiconductor substrate 12 may be doped, undoped or contain doped andundoped regions therein.

At least one isolation region 22 is typically present within with thesemiconductor substrate 12 to provide isolation between devices ofdifferent conductivity. The isolation region 22 may be a trenchisolation region, a field oxide isolation region, or a junctionisolation which are formed utilizing techniques well known in the art.

The gate dielectric 18 is comprised of an insulating material having adielectric constant of about 4.0 or greater, preferably greater than7.0. The dielectric constants mentioned herein are relative to a vacuum,unless otherwise stated. Note that SiO₂ typically has a dielectricconstant that is about 4.0. Specifically, the gate dielectric 18employed in the present invention includes, but is not limited to: anoxide, nitride, oxynitride and/or silicates including metal silicates,aluminates, titanates and nitrides. In one embodiment, it is preferredthat the gate dielectric 18 is comprised of an oxide such as, forexample, SiO₂, nitridized SiO₂, SiO_(x)N_(y), SiN_(x), HfO₂, ZrO₂,Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, Y₂O₃ and mixtures thereof.

The physical thickness of the gate dielectric 18 may vary, buttypically, the gate dielectric has a thickness from about 0.5 to about10 nm, with a thickness from about 0.5 to about 3 nm being more typical.

The gate conductor 20 may comprise single crystal or polysilicon, singlecrystal or poly crystalline SiGe, a silicide, a metal or ametal-silicon-nitride such as Ta—Si—N. Examples of metals that can beused as the gate conductor 20 include, but are not limited to: Al, W,Cu, Ti or other like conductive metals. The thickness, i.e., height, ofthe gate conductor 20 may vary depending on the technique used informing the same. Typically, the gate conductor 20 has a verticalthickness from about 20 to about 180 nm, with a thickness from about 40to about 150 nm being more typical.

It is noted that the description that follows assumes that the initialstructure 10 of FIG. 1A is being employed. In some embodiments of thepresent invention, the gate conductor 20 in each of the regions ofdifferent conductivities may include a gate cap (not shown) such as, forexample, SiO₂ or SiN. In yet another embodiment of the presentinvention, no gate cap is employed. The gate conductor 20 may be dopedif desired to change the workfunction of the FET including the sameutilizing a conventional ion implantation technique well known in theart.

FIG. 1B shows the structure of FIG. 1A during the introduction of aninterfacial dopant 24 into at least one of said at least two regions tomodify the surface characteristic within that region to be the same asthat of the other region not including the interfacial dopant. This stepforms an interfacial doped region 25 within the material region that theinterfacial dopant 24 is being introduced. Specifically, interfacialdopant region 25 is formed at or near the surface of the material regionin which the interfacial dopant 24 is being introduced. By ‘at of nearthe surface’, it is meant that the interfacial dopant region 25 ispresent from about 0.5 nm or more from the surface of the materialregion that the interfacial dopant 24 is being introduced. In thespecific illustration provided, the interfacial dopant 24 is introducedinto the doped surface 14A formed in the region 50A including thepatterned gate region 16A. As shown, a block mask 26 is formed over theregion 50B including patterned gate region 16B and first doped surface14B. The block mask 26 prevents the interfacial dopant 24 from beingintroduced into the area that includes the same. The block mask 26,which is formed by conventional deposition, lithography and optionallyetching, may comprise a conventional photoresist material or a hard maskmaterial such as SiN or SiO₂. It is noted that the block mask 26 is notrequired in all instances and, thus its formation is optional.

In the specific embodiment shown in FIG. 1B, the interfacial dopant 24is being introduced by ion implantation or plasma immersion and ittypically has the opposite conductivity than the surface that it isbeing introduced into. For example, when the doped surface is p-type,than the interfacial dopant is n-type. When the doped surface is n-type,the interfacial dopant is p-type. In some embodiments, a neutral speciessuch as, for example, Ge, O, C and/or Si can be used as the interfacialdopant. When neutral species are used, block mask 26 is not typicallyneeded and the neutral species may then be introduced into both firstdoped surfaces 14A and 14B making those two dissimilar surfaces havesimilar surface characteristics. This particular embodiment of thepresent invention is not shown, but would be understood by theillustration provided as well as the foregoing remarks.

When ion implantation is used to introduce the interfacial dopant 24into the material region (in the embodiment shown the material region50A is being doped), the interfacial dopant 24 ions are implanted usingan energy of greater than 0.1 keV, with an energy from about 0.5 toabout 5 keV being more typical. The dosage of the interfacial dopant 24being introduced by ion implantation is typically greater than 1E10atoms/cm², with a dosage from about 1E11 to about 5E14 atoms/cm² beingmore typical. Within the dosages provided above, the interfacial dopantregion 25 typically has an interfacial dopant 24 concentration ofgreater than 1E17 atoms/cm³, with a concentration from about 1E18 toabout 5E19 atoms/cm³ being more typical. It is noted that theinterfacial dopant region 25 can be tuned utilizing other ionimplantation conditions so long as the ion implantation conditions andhence the formation of the interfacial dopant region 25 does notcompromise the performance of the resultant CMOS device. The ionimplantation may occur at nominal room temperature (i.e., 20°-30° C.) orat a substrate temperature greater than 35° C. with a temperature fromabout 100° to about 300° C. being more typical.

When plasma immersion is used to introduce the interfacial dopant 24,the plasma immersion is performed by first providing a plasma thatincludes the interfacial dopant 24. The introduction of the interfacialdopant 24 is then performed utilizing plasma immersion conditions whichare capable of forming the interfacial dopant region 25 at or near thesurface of the material layer in which the interfacial dopant 24 isbeing introduced. Typically, the plasma immersion is performed utilizingstandard operating conditions to achieve similar ion concentrations asstated above via conventional implantation.

FIG. 1C shows another embodiment of the present invention forintroducing the interfacial dopant 24 into one of the material regionsof the structure that is doped or undoped. In this embodiment, amaterial layer 28 containing the interfacial dopant 24 is firstdeposited on the surface of the structure in which the interfacialdopant 24 is to be introduced. A block mask 26 can be formed over otherregions of the structure in which the interfacial dopant 24 is not to beintroduced. The material layer 28 including the interfacial dopant 24 isa sacrificial material such as a doped silicate glass. The materiallayer 28 can be deposited by any conventional deposition process suchas, for example, chemical vapor deposition, plasma enhanced chemicalvapor deposition, evaporation, spin-on coating, and physical vapordeposition. The thickness of the material layer 28 containing theinterfacial dopant 24 may vary.

After depositing the material layer 28 containing the interfacial dopant24 over the material region in which the interfacial dopant is to beintroduced, the material layer 28 including the interfacial dopant 24 isthen annealed under conditions that are effective for causing diffusionof the interfacial dopant 24 from the material layer 28 into thematerial region, e.g., first doped surface 14A, in which surfacecharacteristic modification is required. The annealing may be performedin a furnace or in a chamber in which the material layer 28 wasinitially deposited. The anneal step is performed at a temperature fromabout greater than 550° C. with a temperature from about 900° to about1100° C. being more typical. In addition to the specific types ofannealing mentioned above, the present invention also contemplates rapidthermal annealing, spike annealing, laser annealing and other likeannealing processes which are capable of performing the saidoutdiffusion. After diffusion, the material layer 28 is typicallystripped from the surface of the structure utilizing a conventionalstripping process.

It is noted that the interfacial dopant used in this embodiment changesthe surface characteristic of the region receiving the interfacialdopant such that that modified region has a similar response to surfacepreparation and rate of epitaxial growth as the region that does notinclude the interfacial dopant. In embodiments when a neutral species isused as the interfacial dopant, the neutral species can be introducedinto one or both of the regions including dissimilar surfacecharacteristic to provide surfaces that have similar responses tosurface preparation and rate of subsequent epitaxial growth.

When the block mask 26 is used, the block mask 26 is stripped from thestructure at this point of the present invention utilizing aconventional stripping. The structure is then subjected to a surfacetreatment process such as wet etching, plasma treatment, thermalprocessing, vapor treatment or other like surface treatment processesthat removes undesirable films from the regions in which epitaxialgrowth will subsequently occur. Next, an epitaxial material 30 such as asemiconductor material including Si and SiGe, for example, is then grownon regions 50A and 50B utilizing a conventional epitaxial growthtechnique that is well known in the art. In some embodiments, theepitaxial growth may include isotopically pure precursors. FIG. 1D showsthe structure after the epitaxial growth of material 30. It is notedthat the first doped region 14A including the interfacial doped region25 was modified so as to have the same response to the surface treatmentand rate of epitaxial growth as than of first doped region 14B.Source/drain implantation and annealing may follow the epitaxial growthprocess.

It is noted that the method of the present invention eliminates the needfor forming a sacrificial spacer on the sidewalls of the patterned gateregion which sacrificial spacer is needed in the prior art during theepitaxial growth process.

In some embodiments, the interfacial dopant 24 may be introduced in thegate conductor 20 as well to provide that material region with theinterfacial dopant region 25. During epitaxy, interfacial dopant region25 within the gate conductor can be used to prevent growth of theepitaxy material atop the gate conductor 20 thus avoiding the need for agate cap.

FIGS. 2A-2C are pictorial representations (through cross sectionalviews) depicting the basic processing steps that are employed in yetanother embodiment of the present invention. In this embodiment, theinterfacial dopant is introduced into surfaces of a structure that havesimilar surface characteristics, i.e., the same response to surfacepreparation and rate of epitaxial growth. The drawings provided in thesefigures are simplistic showing no device details. For example, FIG. 2Ashows an initial structure 10′ including material regions 50A and 50B(doped or undoped), both having the same surface characteristics, i.e.,the same response to surface treatment and rate of epitaxial growth.FIG. 2B shows the structure after introducing the interfacial dopantinto one of the regions forming the interfacial dopant region 25 withinthat region. Illustratively, the interfacial doped region 25 isintroduced in first region 50A so as to modify that region such that itssurface characteristic is different from that of region 50B. One of theabove-mentioned techniques can be used in forming the interfacial dopedregion 25. FIG. 2C shows the structure after epitaxial growth. As shown,the epitaxial material 30 does not form in the region 50A including theinterfacial doped region 25.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of fabricating a semiconductor structure comprising:providing a structure having at least two semiconductor regions, whereinsaid at least two semiconductor regions have dissimilar surfacecharacteristics in terms of their response to surface treatments andrate of epitaxial growth; and introducing an interfacial dopant into atleast one of said at least two semiconductor regions to modify thesurface characteristics within that semiconductor region to be the sameas the surface characteristics of the rest of said at least twosemiconductor regions that does not include said interfacial dopant. 2.The method of claim 1 wherein one of said at least two semiconductorregions comprises a p-type dopant region.
 3. The method of claim 2wherein said interfacial dopant that is introduced into said at leastone of said at least two semiconductor regions is n-type.
 4. The methodof claim 1 wherein one of said at least two semiconductor regionscomprises an n-type dopant region.
 5. The method of claim 4 wherein saidinterfacial dopant that is introduced into said at least one of said atleast two semiconductor regions is p-type.
 6. The method of claim 1wherein said interfacial dopant is a counterdopant ion or a neutralspecies.
 7. The method of claim 6 wherein said interfacial dopant issaid neutral species selected from the group consisting of Ge, O, C andcombinations thereof.
 8. The method of claim 6 wherein said interfacialdopant is said neutral species and is introduced into both an n-dopanttype region and a p-dopant type region.
 9. The method of claim 1 whereinsaid interfacial dopant provides an interfacial dopant region at or neara surface of the semiconductor region in which said interfacial dopantis introduced such that epitaxial growth of a material over saidsemiconductor region including the interfacial dopant region isinhibited.
 10. The method of claim 1 wherein said interfacial dopantprovides an interfacial dopant region at or near a surface of thesemiconductor region in which said interfacial dopant is introduced suchthat epitaxial growth of a material over said semiconductor regionincluding the interfacial dopant region is promoted.
 11. The method ofclaim 1 wherein said at least one of said at least two semiconductorregions includes a doped surface and is selected from the source/drainregion, the gate region or both of a field effect transistor.
 12. Amethod of fabricating a semiconductor structure comprising: providing asemiconductor substrate having a first doped surface of a firstconductivity type and a second dopant surface of a second conductivitytype, said first conductivity type differs from said second conductivitytype; introducing an interfacial dopant into at least one of said dopedsurfaces to provide said surface including the interfacial dopant withsame surface characteristics as that of the other doped surface notincluding said interfacial dopant; and epitaxial growing a semiconductormaterial from said doped surfaces, wherein an interfacial dopant regionis present in said doped surface in which said interfacial dopant wasintroduced that separates said semiconductor material from said dopedsurface.
 13. The method of claim 12 wherein said interfacial doped is acounterdopant ion or a neutral species.
 14. The method of claim 12wherein said introducing of said interfacial dopant is by ionimplantation, plasma immersion or outdiffiision from a material layerincluding said interfacial dopant.